1. Field of Invention
The present invention relates to a method of testing semiconductor integrated circuits (ICs). More particularly, the present invention relates to a method of testing a ball grid array (BGA) IC package.
2. Description of Related Art
Ball grid array integrated circuit (BGA IC) represents new generations of a method of high pin count IC packaging. BGA IC is suitable for packaging ultra-large scale integration (ULSI) chips having sub-micron resolution. As integrated circuits become functionally more powerful, the number of output pins demanded by each silicon chip increases, too. Conventional packaging methods such as quad flat pack (QFP) or pin-grid array (PGA) are gradually unable to provide a greater number of pin counts. Common QFP or PGA packages these days can provide from over a hundred to about two hundred IC leads. However, a current logic IC chip may demand more than three hundred leads.
For example, the core logic of a 64-bit microprocessor based personal computer must be capable of connecting the microprocessor with system memories such as DRAM or flash SRAM through a fill 64-bit wide bus. If the core logic circuit is fabricated on an IC chip, data bus and address bus output from the IC chip must occupy at least two hundred pins. Together with other controlling signal leads, more than three hundred pins are often necessary for packaging the chip. Hence, only a BGA IC type of packaging is capable of satisfying the high pin count requirements.
FIG. 1 is a flow diagram showing the conventional testing procedure of a BGA IC package. As shown in FIG. 1, conventional BGA IC packages are tested following the sequence from steps (a) through (e).
In step (a), a BGA IC package 100 having no attached solder balls is provided. In other words, substrate 102 of the BGA IC package 100 does not have any solder balls attached. In FIG. 1, the silicon chip is labeled 101 while the landings on the substrate for making electrical contact are labeled 103.
In step (b), solder balls 104 are attached to the landings 103 on the substrate 102 of the BGA IC package 100.
In step (c), the BGA IC package 100 having attached solder balls 104 is mounted onto a burn-in (B/I) test socket 105. During the B/I testing, the solder balls 104 must remain attached to test contacts 106 of the B/I test socket 105.
In step (d), the BGA IC package 100 having attached solder balls 104 is transferred to a final test socket 107 for final testing. During the final testing, the solder balls 104 must also remain attached to test contacts 108 of the final test socket 107.
Finally, in step (e), when testing shows no defects in the chip, the BGA IC package 100 is mounted onto a printed circuit board (PCB) 109 by using a surface mount technique.
In the aforementioned BGA IC testing method, the test contacts 106 within the B/I test socket 105 must attach to the solder balls 104. However, during burn-in testing, a lot of heat is generated, and hence the following defects are produced:
1. Solder balls may be damaged resulting in defective soldering joints when the BGA IC package is mounted onto a PCB. PA1 2. Some solder may melt and stick on the point of attachment of the test contacts. Hence, the working life of the B/I test socket may be shortened.
In light of the foregoing, there is a need to provide an improved method of testing the chip inside a BGA IC package.